Electrolytic cell apparatus for the destruction of odorous impurities in a gas stream

ABSTRACT

In combination with a contact zone for the mass transfer of pollutant or odorous materials from a gas stream to an aqueous acid stream containing Co(III), the Co(III) oxidizing the pollutant or odorous materials and itself becoming reduced to Co(II), there is provided electrolytic regeneration apparatus for the continuous electrolytic regeneration of Co(II) to Co(III). Pollutant or odorous materials are also continuously destroyed at the electrodes of the electrolytic regeneration apparatus. The electrolytic regeneration apparatus comprises a Co(III) and acid-resistant container to receive the Co(III)-acid stream wth lead anodes and cathodes supported in the interior of the container which contact the Co(III)-acid stream during electrolytic regeneration of Co(III) and pollutant destruction. The area of the anodes is such that upon the passage of electrical current through the electrolytic apparatus the regeneration of Co(III) from Co(II) in the aqueous acid stream is the predominant reaction therein.

United States Patent 1191 Za'bolotny ELECTROLYTIC CELL APPARATUS FOR THE DESTRUCTION OF ODOROUS IMPURITIES IN A GAS STREAM [75] lnventor: Ernest R. Zabolotny, Syracuse, NY.

[73] Assignee: Carrier Corporation, Syracuse, NY.

[22] Filed: Sept. 4, 1970 [21] Appl. No.: 69,641

References Cited I UNITED STATES PATENTS [.111 3,755,130 1451 Aug. 28, 1973 Primary Examiner-John H. Mack Assistant Examiner-D. R. Valentine Attorney-Sughrue, Rothwell, Mion, Zinn and Macpeak I [57] I ABSTRACT In combination with a contact zone for the mass transthe electrodes of the electrolytic regeneration appara- The electrolytic regeneration apparatus comprises a Co(lII) and acid-resistant container to receive the Co(lll)-acid stream wth lead anodes and cathodes 1,032,623 7/1912 Reed 204/292 X 1457,51 7/1969 Konejarvi 204,242 X supported 1n the mterror of the container whlch contact 2,852,463 9/1958 Gutzmer... 204/242 the mb- Stream during electrolytic 3,441,495 4/1969 Colman 204/290 F regeneration of Co( 111) and pollutant destruction. The 3,598,715 8/1971 Goens et al. 204/290 F area of the anodes-is such that upon the passage of 3,403,091 968 Currey t a1 204/242 electrical current through the electrolytic apparatus 3,405,051 10/1968 Crane 204/275 X the regeneration of from in the aqueous FORHGN PATENTS 0R APPLICATIONS acid stream is the predominant reaction therein. 682,411 3/1964 Canada 204/130 4 Claims, 2 Drawing Figures PATENTEDMIB28 I975 3,755, 130

FIG. I

NV ENTOR ERNES. v ZABOLOTNY ELECTROLYTIC CEIJL APPARATUS FOR TH DESTRUCTION OF ODOROUS IMPURITIES. IN A GAS STREAM BACKGROUND OF THE INVENTION 1. Field of the Invention I The present invention relates to apparatus for the electrolytic regenerationofCoflII) from Co(II) and for the electrolytic destructionof pol-lutant-or odorous materials.

2. Description-of the Prior Art- Electrolytic cells are well known to the prior art. However, the prior art has never utilized an electrolytic cell for the destruction, atthe electrodesthereof, of

pollutant or-odorous materials cleansedfrom a gas stream.

Further, the prior arthas'never utilized 'an'electrm lytic cell forthe electrolytic regeneration of Co(lll) carried in an aqueous acidstream, whichCo(III) has a streamused to destroy-pollutantor odorous materi als,=no rof usage for the actual destruction"of po llutant or odorous materials'at theelectrodes of *suchacell.

The prior art, as typified by U.S. Pat; No. 3,259,560,.

Brandes et al, is aware :of processes and apparatus'for the-electrolytic production'of chromium from afluoride'bath usinganianode of 'a metal or'alloyth'atis not attacked'fbythe'electrolyte. While'the anode cancom prise. a precious/metal coated with lead oxide, there is notappreciation'of utility for the pollutioncontrol environment.

Electrolytic cells,=- as disclosed in US: Pat. No; 3,455,811, Bender et al, are also known wherein'lead or lead-alloy anodes are used for the anodic oxidation of dissolved manganous salts; i.e., manganous sulphate in sulfuric acid. However,- no teaching of apparatus for use 'in I the pollution 'control environment is taught or suggested therein.

SUMMARY OF THE INVENTION In 'combination' witha -contact'zone forthe rriass transfer ofpollutant or *odorous materials from" a gas stream to anaqueous'acid'stream containing. Co(lIl"), the Co(lll) oxidizing the pollutant or odorous'materia'ls and itselfbecomi'n'g*reduced to Co("), there is" provided electrolytic regenerationapparatus for the continuous' electrolyticregeneration of Co(II)to Co(lll); Pollutant or odorous materials are'also continuously destroyed at-the electrodes of the-electrolytic-regenera tion apparatus. i I

The electrolytic regeneration apparatus specificall comprises a Co(III and acid-resistant container to receive the"Co(III)'-acid =stream =with at team": lead anode and'one lead cathode-supported'in' the interior of the container." Th'e areaof the-anode" issuch that uponthe passage-of electrical 'currentthrough'the apparatus the regeneration of Co(III) from Co() is the erence.

predominant reaction therein. Electrical connections joining the anode and cathode, in electrical circuit, to an electrical power supplymeans are also provided. During electrolytic regeneration pollutant or odorous materials are destroyed at the electrodes of the electrolytic pparatus. 5 Li.

It is one object of this invention to provide improved apparatus for the destruction of pollutant or odorous materials;

It is a further object of the present invention to provide electrolytic regeneration apparatus for the destruction of pollutant or odorous materials. at the electrodes thereof which simultaneously accomplishes the electrolytic regeneration of Co(), carried in an aqueous acid stream, to Co(lll).

These and other objects of the present invention will be explained in greater detail in the following material.

BRIEF DESCRIPTION OF THE DRAWINGS DETAILED DESCRIPTION. OF THE PREFERRED EMBODIMENTS The electrolytic regeneration apparatus of this invention finds particular usage in the process described in co-pending United States Ser. No. 69,804, tiled Sept. 4', 1970, in the names of Elabolotny, P. Chang and W. Biermann, entitled Process and Apparatus for Removirig Pollutants From Gas Streams. This copending United States application is hereby incorporated by ref- Before entering into a detailed description of the electrolytic regeneration apparatus of this invention, it

is appropriate to briefly indicate theprocessing background wherein the apparatus of this invention finds particular application. I

As described in the above identified copending United States application, it has been discovered that pollutant and odorous materials can be removed from agas stream, and destroyed by oxidation, by contacting the gas'stream with an aqueous acid streamcontaining the elevated valence form of cobalt, i.e., Co(lll). Contacting can take place in any state of the art apparatus whichinsures adequate mass transfer of the pollutant or odorous'materia ls (hereinafter referred to as pollutant materials) to the aqueous acid stream for contact with the Co( III) carried therein (hereinafter this stream is" referred to as the Co(lll).-acid stream), whether the mass transfer'be by absorption into the Co(III)-acid stream or by adsorption onto the surface of the Co(lll)- a'eidstrearn. For instance, packed bedsfspray towers,

verituri ejectors, and the like can be used. The principles of mass transfer are well known to the art, and any qualified chemical engineer can determine the exact contact apparatus most well suited for any particular process operation. r

The gas stream containing the pollutant materials (hereinafter the gas stream) can be from any source which contains pollutant materials which are oxidiz able, and suchmaterials will be apparent to one skilled in the art, for instance, organic materials such as form aldehyde and inorganic materials such as hydrogen sulfide are commonly encountered.

During the above described oxidation the Co(lll) is reduced to Co(II), and to achieve a commercially practical process it is necessary to regenerate, or convert, Co(II) to'Co(IIl) for further pollutant oxidation.

The acid used to form the Co(lII)-acid stream must, of course, be one which permits Co(III) to be electrolytically regenerated from Co("). The mineral acids are-preferred for usage as the acid of the Co(III)-acid stream, with sulphuric, phosphoric and perchloric being preferred. Sulphuric acid is most preferred. Salts of acids can be utilized to provide the Co(lII)-acid stream, either alone, or in combination with acids. If an 'acid is acceptable, its salt can also be used. The pH of the aqueous acid stream should be less than 1, and the normality should be less than 27.5 to permit electrolytic regeneration of Co( III).

The Co(II) may initially be introduced into the acid in a number of ways. Introduction may be accomplished by adding the required amount of Co(II) to the acid in the form of a cobaltic salt which is dissolved by the acid. The exact form in which cobalt is introduced is not overly important, so long as Co(II) is provided.

The total amount of Co(lll) which is required in the system of the present invention is most appropriately described with reference to the rate at which Co(lII) must be regenerated. This is because the total cobalt in the system is present as both Co(II) and Co(lll) and, of course, there is a constant conversion of Co(II) to Co- (III) during electrolytic regeneration and a constant conversion of Co(III) to Co(") during pollutant oxidation.

It is preferred that Co( Ill) be in dynamic equilibrium with the pollutant materials. That is, the Co(lII) should be regenerated at a rate at least equal to the rate at which Co(III) is consumed in the oxidation of pollutant materials.

It should be understood that as long as any Co(III) can be detected in the Co(III)-acid stream, some oxidation of pollutant materials will occur. However, for practical usage, the total cobalt concentration should be greater than 0.002 molar to achieve detectable oxidation.

Having thus generally described operable acids and the factors involved in determining the amounts of cobalt required, the following discussion will be in terms of what has been found to be a most preferred aqueous acid stream, i.e., sulphuric acid at a pH less than 1 and at a normality no greater than about 27.5 containing Co(lII) which is produced during electrolytic regeneration at a rate so as to be in dynamic equilibrium in the system. Most preferably the total cobalt concentration of the aqueous acid stream is greater than 0.005 molar, and can be up to the saturation point of cobalt.

Electrolytic regeneration apparatus is required in pollution control processes as described for two reasons. First, regeneration is rapid and efiicient. Second, destruction of pollutant materials occurs at the electrodes of the regeneration cell. Thus, a simplified means for a continuous pollution control process is provided with improved destruction of pollutants.

Electrolytic regeneration of the type of the Co(lIl)- acid stream under consideration is complicated by several factors. One of the most important of these factors is that the aqueous acid stream used is extremely reactive, which can lead to failure of process equipment atpoints in direct contact with the aqueous acid stream. The problem of cell destruction is encountered with the Co(III)/sulphuric acid system because of the extremely high reactivity of Co(III).

It has been found that for the Co(lII)-sulphuric acid system, few of the common electrode materials used by the prior art in electrolytic cells are operable for long term regeneration.

Many materials were tested to find acceptable electrodes. For the cathode, almost all materials except uncoated copper were found to work well for short periods of time. For instance, nickel, nickel alloys, copper (as long as totally coated by the Co(III)-acid stream), lead coated copper, aluminum, titanium, 304 stainless steel and tantalum were found to be operable for short periods of time. However, rather unexpectedly, only platinum coated titanium and lead were found to be operable for extended periods of time.

The problem of electrode life was more pronounced in finding a material which could be used as an anode for the Co(lII)-sulphuric acid system. Tantalum, tungsten and titanium rapidly passivated and blocked current in the cell. Such must'be avoided. For long term operation, molybdenum and copper, even lead coated copper, were found to eventually erode and require re placement. Lead and platinum coated titanium were found to be economically feasible for long term commercial operation.

Balancing cost factors involved, the preferred anode/cathode assembly is thus a lead-lead system. While the anode isinitially lead, a rapid coating of lead dioxidelforms on the anode. For some reasons, this anode does not function well until this lead dioxide coating forms. It is theorized that lead dioxide acts as a protective film to stop the conversion of elemental lead to Pb(II).

It will be apparent to one skilled in the art that the acceptability 'of any particular anode/cathode arrangement for the electrolytic regeneration/pollutant material destruction apparatus of this invention will depend upon the degree of reliability required for the term of operation contemplated. Accordingly, equivalents to the above materials will be determinable by one skilled in the art in accordance with the knowledge made available by the present specification.

In view of the reactivity of the Co(III)-sulphuric acid system, care must be taken in fabricating the interconnecting electrical members utilized. Because of the easy fabricability of copper, one may use a resin coated copper for all interconnections in the cell. Polyvinyl chloride has been found to be very useful for protecting the copper interconnections. For long term reliability, at /40 to 40/60, preferably 50/50, tin/lead solder can be used to attach the anodes and cathodes to the resin protected copper interconnected members.

The anodes and cathodes should be'correlated'so as to maximize the anode reactions, i.e., the'eonversion of Co(II) to Co(III), and to minimize the cathode reactions, i.e., Co(IIl) to Co(II). A determination of the optimum anode/cathode area for any particular unit can easily be determined by one skilled in the art. For instance, an anode/cathode area ratio of 20:1 can be used.

Reference should now be made to FIG. 1 of the drawings which shows the electrolytic regeneration cell of this invention in use in a pollution control process. The contact zone, which preferably is a packed bed, is

represented by numeral 1. The Co(llI)-acid stream is introduced into the contact bed via line 2 where the Co(llI)-acid stream is intimately contacted with the upflowing gas stream which enters via line 3. Contact occurs as the acid trickles and flows over the packing 4. The contacting achieves maximum mass transfer of the pollutant materials into, or onto, the Co(llI)-acid stream.

After contacting, the gas stream with a reduced pollutant content exits via line 5 and the Co(llI)-acid stream, containing an increased amount of pollutants, is removed by pump P via line 6 and forwarded to electrolytic regeneration cell 7 in accordance with the present invention. After regeneration, the Co(lll)-acid stream is removed and recycled to the contact means via line 2. Power supply means 8 for the cell is also shown.

Turning now to FIG. 2, there is shown therein a cross sectional view of an electrolytic regeneration cell in accordance with the present invention. The electrolytic regeneration apparatus comprises casing 10 which is provided with entrance port 11 and exit port 12 for the Co(llI)-acid stream before and after regeneration, respectively. Vertically extending support member 13 is shown in combination with horizontally extending support member 14. Depending from the horizontally extending support member 14 in a downward direction are the anodes l6 and the cathodes l7soldered into the horizontally extending support member 14 by 50/50 lead/tin solder 15. i

The casing 10 is formed of glass reinforced polyester, members 13 and 14 are polyvinyl chloride coated copper, and members 16 and 17 are initially leadjA cell as described was used in the example.

During regeneration, the level of the Co(llI)-acid stream in the cell is maintained so as to substantially cover the anodes and cathodes. The configuration of the electrodes are such that good circulation is provided in the cell, i.e., so that the Co(llI)-acid stream may sufficiently contact the electrodes to permit efficient regeneration. One acceptable configuration can be as shown in FIG. 2. However, it shall be understood that the exact configuration of the anodes, cathodes, etc., is of no critical importance so long as the desired rate of regeneration and destruction of pollutants at the electrodes can be achieved. The electrodes can, for instance, be solid sheets, mesh, discs, either solid or perforated, etc.

To regenerate 17 gallons per minute of a Co(llI)- sulphuric acid stream (45 percent acid at a pH below 1, containing 0.1M cobalt) used to treat 2,000 cfm of a waste gas issuing from a rendering plant containing 30 ppm of oxidizable impurities, 2.8 X 10 M/min. of Co(llI) were regenerated in a cell as heretofore described. An anode current density of 0.8 to 1.1 X 10 amps/cm, a cathode current density of 0.264 amps/cm, and an anode/cathode area ratio of 20:] were used. The total anode area was 27,000-38,000 square centimeters and operation was at ambient temperature, i.e., 80110 F, and ambient pressure. A power supply of 300 amps was required for the regeneration at coulombic efficiency of 30-40 percent. The

. oxidizable impurities destroyed in the process were While the invention has been particularly shown and described with reference to preferred embodiments thereof, it will be understood by those skilled in the art that various changes in form and details may be made therein without departing from the spirit and scope of the invention.

What is claimed is:

1. In combination, apparatus for the continuous removal and destruction of pollutant materials contained in a gas stream comprising:

A.. contacting means comprising a packed bed for continuously contacting a gas stream containing pollutant materials with an aqueous sulfuric acid stream containing Co(ll) and Co(lll), said pollutant materials being transferred to said aqueous sulfuric acid stream by said contacting;

B. electrolytic regeneration and pollutant destruction apparatus for continuously destroying said pollutants at the electrodes thereof and continuously regenerating said Co(lll) from said Co(ll);

C. a first conduit means communicating between said contacting means and said electrolytic apparatus for continuously removing said aqueous sulfuric acid stream containing said pollutant materials from said contacting means and continuously feeda ing said stream to said electrolytic apparatus; and

D. a second conduit means communicating between said electrolytic apparatus and said contacting means for continuously returning said aqueous sulfuric acid stream to said contacting means for Co- (III) regeneration and pollutant destruction in said electrolytic apparatus; said electrolytic regeneration and pollutant destruction apparatus comprising a. a sulfuric acid and Co( 111) resistant container comprising glass reinforced polyester; b. at least one anode and at least one cathode supported within said container in positions whereby said anode and cathode contact said aqueous sulfuric acid stream containing said pollutant materials continuously fed to said container, said anode and said cathode being comprised of a material selected from the group consisting of platinum-coated titanium and lead, wherein the ratio of the anode area/cathode area is 20/1 such that upon the passage of electrical current through said electrical apparatus, regeneration of Co( 111) from Co(ll) is the predominant reaction thereon;

c. an electrical power supply means; and d. horizontally extending electrical connection means within said container comprising support members of polyvinyl chloride-coated copper joining said anode and cathode in an electrical circuit to said electrical power supply means, said anode and cathode being joined to said support member by means of a solder which comprises tin and lead within a tin/lead weight ratio of from 60/40 to 40/60. 2. The combination according to claim 1 in which the anode is lead and carries a coating of lead dioxide.

3. The combination according to claim 2 wherein the anode and cathode are lead.

4. The combination according to claim 1 wherein the anode and cathode are platinum coated titanium. 

2. The combination according to claim 1 in which the anode is lead and carries a coating of lead dioxide.
 3. The combination according to claim 2 wherein the anode and cathode are lead.
 4. The combination according to claim 1 wherein the anode and cathode are platinum coated titanium. 